Make the filling. In a large skillet over medium heat, melt butter. Add diced onion, season with salt, and cook for a few minutes until softened and translucent. Add diced Honeycrisp apples, minced garlic, and fresh herbs. Cook for another 30 seconds until fragrant. Don't overcook the apples - they'll continue cooking inside the pork! Remove from heat, place in a bowl, and stir in apple butter and Dijon mustard until well combined. Season with black pepper. Set aside to cool.
2 tablespoons unsalted butter, 1 small yellow onion, ¼ teaspoon kosher salt, 2 small Honeycrisp apples, 10 cloves garlic, 1 tablespoon fresh thyme, 1 tablespoon fresh rosemary, 1 tablespoon fresh sage, 2 tablespoons apple butter, 2 tablespoons Dijon mustard, ¼ teaspoon black pepper
Butterfly the pork. Place pork loin fat-side up on a cutting board. Using a sharp knife, make a horizontal cut along the length, starting ½ inch from the bottom and cutting almost all the way through, leaving ½ inch intact. Open like a book and continue to cut and roll, being careful not to cut all the way through. Make additional cuts in thicker sections to create a more even thickness. Cover with parchment or plastic wrap and use a meat mallet to pound into an even 1-inch thickness throughout.
3-4 pound pork loin roast
Season the pork. Mix together garlic powder, onion powder, dried thyme, sage, rosemary, smoked paprika, dried mustard powder, black pepper, cayenne (if using), and salt. Season the pork generously on all sides.
1 tablespoon kosher salt, 2 teaspoons garlic powder, 2 teaspoons onion powder, 2 teaspoons dried thyme, 2 teaspoons dried rosemary, 1 teaspoon smoked paprika, 1 teaspoon dried sage, 1 teaspoon dried mustard powder, 1 teaspoon black pepper, ¼ teaspoon cayenne
Stuff and roll. Spread cooled apple filling evenly over the interior of the pork, leaving a 1-inch border around edges. Starting from one long side, roll up tightly, keeping filling tucked inside. Make the roast as tight as possible for even cooking.
Tie the roast. Tie with kitchen twine at 1-2 inch intervals, making sure ties are snug but not cutting into the meat. Cut off excess twine.
Sear the pork. Heat oil in a large skillet over medium-high heat. When hot and shimmering, sear the stuffed pork on all sides until deeply golden brown, about 2-3 minutes per side. Remove and set aside. Preheat oven to 375°F.
2 tablespoons oil
Cook the aromatics. In the same skillet, melt butter over medium heat. Add sliced onions, season with salt, and cook 5-7 minutes until beginning to soften. Add smashed garlic and cook another couple minutes. Add fresh herb sprigs, bay leaves, apple cider, and chicken stock, scraping up browned bits from the bottom.
2 tablespoons butter, 2 large yellow onions, 10-12 cloves garlic, ¼ teaspoon kosher salt, black pepper, 1 cup apple cider, 1 cup chicken stock, 2-3 sprigs fresh thyme, 2-3 sprigs fresh rosemary, 2-3 sprigs fresh sage, 2-3 bay leaves
Roast the pork. Nestle the seared pork back into the pan on top of the onions. Liquid should be about ½ to 1 inch deep. Cover and transfer to a preheated 375°F oven. Roast covered for 45 minutes, then remove lid or foil and continue roasting uncovered until internal temperature reaches 145°F. Total cook time is 60-90 minutes (about 18-23 minutes per pound).
Rest the pork. Transfer pork to a cutting board, tent with foil, and rest 10-15 minutes.
Make the gravy. Strain pan liquid through a fine-mesh sieve into a measuring cup (reserve onions and garlic if desired for serving). Don't skim the fat. In the same skillet, melt butter over medium heat, add flour, and whisk constantly for 1-2 minutes until it forms a smooth roux and smells slightly nutty. Gradually whisk in strained drippings and dchicken broth. Add Dijon and Worcestershire. Season with salt and pepper. Simmer 5-8 minutes until thickened, whisking occasionally. Add chicken broth if needed to thin.
4 tablespoons butter, 4 tablespoons all-purpose flour, 1.5-2 cups pan drippings, 1½ tablespoons Dijon mustard, 2 teaspoons Worcestershire sauce, salt and pepper, 1-2 cups chicken broth
Slice and serve. Remove twine from pork and slice into ¾ to 1-inch rounds. Serve on a bed of mashed potatoes with green beans and reserved onions if desired. Drizzle with plenty of apple cider gravy!